Net::SSH::Perl::SSH2 implements the SSH2 protocol. It is a subclass of Net::SSH::Perl, and implements the interface described in the documentation for that module. In fact, your usage of this module should be completely transparent; simply specify the proper protocol value (2) when creating your Net::SSH::Perl object, and the SSH2 implementation will be loaded automatically.

NOTE: Of course, this is still subject to protocol negotiation with the server; if the server doesn't support SSH2, there's not much the client can do, and you'll get a fatal error if you use the above protocol specification (2).